1. Field of the Invention
This invention relates to an integrated technology in sequential treatment of organics and heavy metal ions wastewater, particularly to one capable of firstly using a fenton process to remove organics from wastewater, and sequentially using a ferrite process to remove multiple heavy metal ions from the wastewater in order to increase the quality of ferrite products obtained therefrom. By controlling pH, temperature and ferrous salt, Fe ions taken as catalysts in the fenton process under acidic conditions are turned into reactants in the ferrite process under alkaline conditions, thereby reducing the amount of iron sludge caused in the fenton process, decreasing a reaction time of the ferrite process, increasing the quality of ferrite products obtained therefrom for recycling, and enhancing an efficiency in solid/liquid separation.
2. Description of the Prior Art
Although some conventional treatment processes can treat industrial wastewater to make the water quality met with the limitations of the environmental laws, sludge with heavy metal oxides caused by such conventional wastewater treatments becomes a serious secondary pollution needed to be solved further. For example, there is a large amount of heavy metal sludge generated per year and becoming hazardous industrial waste. Although the heavy metal sludge is currently treated by approved solidification, solidified matrix formed therefrom cause an overloading to landfills, or even become a source of soil pollution.
Since the wastewater of a surface finishing plant (e.g., electroplating wastewater) generally contains heavy metal ions and low biodegradable organics (e.g., surfactants), the current wastewater treatment can use a fenton process to treat the low biodegradable organics and a ferrite process to treat the heavy metal ions, respectively.
1. At the moment, the fenton process is generally used to treat many low biodegradable organics such as phenols, chlorophenols, chlorobenzenes, nitrophenols, nitrobenzenes, hydrocarbons, polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated ethylenes (PCEs), and surfactants, etc., and has an ability of treating the organics with high concentration up to 175,000 ppm. Moreover, since the fenton process is a homogeneous catalytic reaction without limitation in mass transfer, reactor tanks used in the fenton process can be easily designed in the treatment of wastewater. In addition, the fenton process also performs well in the decoloration of dyeing wastewater by lowering the absorption of the organics to ultraviolet rays in an ultraviolet/hydrogen peroxide (UV/H2O2) treatment.
However, there are disadvantages incurred in the fenton process because of some limitations, e.g., an increasing reaction time due to the insufficient Fe ions, and an iron sludge production caused by a chemical coagulation of the Fe ions, which are described as follows.
(1). Since the fenton process is performed under acidic conditions of pH in the range of 2˜5, it is unsuitable for the fenton process to treat soil and sludge in alkaline and buffer environment.
(2). Traditionally, in the fenton process, a fenton's reagent, a mixture of ferrous salt and hydrogen peroxide (H.sub.2O.sub.2), is added into the wastewater. The ferrous salt including ferrous ions (Fe.sup.2+) and ferric ions (Fe.sup.3+) is taken as a catalyst, and more or less amount of the catalyst has a greater effect on the terminal time of the fenton process. However, since the hydrogen peroxide (H.sub.2O.sub.2) can make the ferrous ions (Fe.sup.2+) turned into ferric ions (Fe.sup.3+), all of the Fe ions are required to be further removed by the chemical coagulation. A large amount of iron sludge caused in the treatment of the Fe ions by the chemical coagulation also becomes an overloading of landfills. Moreover, in case of the wastewater contains heavy metal ions therein, heavy metals are liable to be dissolved from heavy metal sludge under acidic conditions to make the heavy metal sludge become a hazardous industrial waste required to be further treated by solidification, thus increasing the cost for the treatment of such hazardous industrial waste.
(3). In order to reduce the iron sludge production in the fenton process, less amount of the catalyst is applied to the wastewater, thus resulting in an extension of the reaction time for extra several hours.
Therefore, the traditional fenton process is disadvangeous because the Fe ions taken as catalysts have to be removed by the chemical coagulation, and such large amount of iron sludge caused in the removal of the Fe ions is needed to be treated further, thus increasing the reaction time and the cost of wastewater treatment.
In order to solve the problem of the iron sludge, a Fered-Fenton technology is used to oxidize and decompose the organics of the wastewater without using a large amount of the ferrous salt. However, the Fered-Fenton technology requires a longer reaction time, thus becoming uneconomical in cost.
Furthermore, a fluidized bed is used to make the Fe ions coated onto a support to reduce the iron sludge production. However, after the surface of the support being coated with the Fe ions, the support will be expanded too large to perform the function of the fluidized bed any further, thus limiting the capacity of reducing the iron sludge production.
2. The ferrite process, as a chemical precipitation of hydrometallurgy technology, is commonly used by those skilled in the art to treat heavy metal wastewater containing multiple heavy metal ions, e.g., As, Ba, Cd, Cu, Co, Cr, Fe, Mn, Hg, Mo, Ni, Pb, Sr, V, Zn, etc., and has an ability to treat such heavy metal ions with high concentration up to 20,000 ppm so that the ferrite process is also suitable to be widely utilized in the treatment of heavy metal wastewater such as laboratory wastewater, acid mining drainage, surface finishing wastewater, and stainless steel processing wastewater, etc.
However, the ferrite process requires to have sufficient amount of reactants including ferrous ions (Fe.sup.2+) and ferric ions (Fe.sup.3+) added into the wastewater to form ferrite products, by which the hazardous heavy metal ions are stabilized in the crystal lattices of the ferrites without worry of being leached to cause soil pollutions.
In the existing ferrite process, a proper amount of the ferrous salt is added into the wastewater to be oxidized by air for forming the ferrite products provided with high stability and capable of being passed the limitation of Toxicity Characteristic Leaching Procedure (TCLP). Moreover, the ferrite products with magnetism can be recycled as magnetic materials for further use. However, some organics contained in the wastewater have a harmful effect on the magnetism of the ferrite products, thus greatly decreasing the quality of the ferrite products to be recycled as industrial raw materials and lowering the economical incentive of encouraging the skilled in the art to recover the ferrite products for reuse due to their low quality.
Based on the aforesaid description, it is apparent that the heavy metal ions and the low biodegradable organics contained in the mixed wastewater of the surface finishing plant are unable to be simultaneously removed from the wastewater either by a fenton process or a ferrite process. Therefore, a more effective solution is required in the low cost of wastewater treatment and the high economical valve for reuse.
In the conventional wastewater treatments using ferrous ions (Fe2+) and hydrogen peroxide (H2O2), one single fenton process is often used to treat wastewater containing low biodegradable organics; one single ferrite process is also often used to treat wastewater containing heavy metal ions. Ferric ions (Fe3+) yielded in the fenton process cause a color problem in the wastewater, but are required for forming ferrite products in the ferrite process. In order to solve the above-mentioned problems, the present invention discloses an integrated technology of the fenton and ferrite processes in sequential treatment of organics and heavy metal ions out of the wastewater, thereby capable of treating wastewater of most surface finishing plants, decreasing treatment units and reducing the amount of iron sludge.